1. Field of the Invention
The present invention relates to a die casting machine or a plastic injection molding machine (hereinafter: die casting machine), and more specifically, relates to the die casting machine provided with a mold clamping apparatus enabling dimensions as small as possible in the direction of opening and closing of a mold, and a method of changing the mold in the die casting machine that is provided with such a mold clamping apparatus.
2. Description of the Related Art
Die casting is a molding method in which melt metal is molded in a mold which is manufactured with high dimensional accuracy. Accordingly, it has a big advantage that a molded article, even with a complicated shape, can be molded in one process, compared with plastic forming such as forging and extruding, or cutting. Therefore, the die casting is suitable for applications where the prices of products are low and the products are mass produced. Such products can have complicated shapes, an can be parts, members, or molded articles of assemblies such as automotive engines that can have mechanical strength.
The mold of the die casting machine which can mold the various kinds of articles mentioned above is often formed by the combination of an insert die defining a cavity corresponding to the shape of each molded article and a main mold fastening and holding the insert die, mainly to reduce production cost, though the cavity can be formed with a single steel material. In the case of the plastic injection molding machine, the mold is also formed by the combination of the insert die and the main mold. Such a main mold, therefore, can be employed with versatility, because it is able to correspond to the insert dies for various kinds of molded articles.
Also, compared with the plastic injection molding machine, the mold for the die casting machine is provided with many core cylinders in the directions of up and down, or right and left, because many cores are used for molding much more complicated molded articles.
Generally, the main mold forming a moving mold mounted on a moving die plate of the die casting machine is provided with more core cylinders than a main mold forming a fixed mold mounted on a fix mold die plate, and includes various constituent elements such as a portion of an extrusion pin for extruding a molded article and pipe lines for supply and drain of the pressurized oil to and from each cylinder, so that it constitutes a complicated formation in which many core cylinders are mounted thereon extended in the up and down, or right and left direction. Accordingly, when each main mold fastening the insert die is mounted on the moving die plate and the fixed die plate respectively, a problem can arise that at least two upper tie bars can disturb the main mold when the at least two upper tie bars are carried in or carried out to and from a working space for mounting by means of a crane, and wherein the working space for mounting is located between the moving die plate and the fixed die plate.
In order to avoid such disturbance, the tie bars are pulled out from both of the die plates, before a mold changing operation. Further, it is necessary to provide cylinders that can be used to only pull out the tie bars in the die casting machine. This can cause a problem in that the dimension of the mold clamping apparatus in the direction of opening and closing of the mold must be increased in order to secure an adequate working space.
FIG. 5 is a flow chart that illustrates a series of work sequences for a mold changing operation in the prior art described above. As shown in FIG. 5, the tie bar is pulled out from a fixed die plate, in step 5. In step 9, the tie bar is inserted into the fixed die plate. However, there arises a problem in that it takes considerable amount of time to move the tie bar for pulling out the fixed die plate and inserting therein because the tie bar has a large amount of weight.
Also, in the prior art, the main mold and the insert die are carried in or carried out to and from the die casting machine, wherein the main mold and the insert die are attached fixedly on or detached from the opposing surface of each die plate. In order to reduce the total time elapsed for the mold changing operation, the fastening or unfastening of the insert die to or from the main mold can be performed outside the die casting machine prior to and after the mold changing operation.
FIG. 4 illustrates a configuration wherein a pair of main molds MVD and FXD are carried in a mold open space together with the inserts by means of the crane after the upper tie bars TBU are pulled out. The mold open space is defined as a space formed between the mounting surfaces of a moving die plate MVPL and a fixed die plate FXPL, when the moving die plate MVPL retracts from the fixed die plate FXPL by a predetermined distance.
In FIG. 4, reference code TBU designates the upper tie bar, and reference codes CYL 1, CYL 2 and CYL 3 designate cylinders for the cores which are mounted on the main mold MVD and fastened on the mold mounting surface of the moving die plate MVPL. Reference codes MINS and FINS are a pair of insert dies fastened in the main mold MVD and the main mold FXD.
In FIG. 4, a die length is defined as the distance between both of the mold mounting surfaces when the moving die plate MVPL reaches a mold closing position by moving in the right direction such that the main molds MVD and FXD are each fastened on the mold mounting surface of the moving die plate and the fixed die plate, respectively. In FIG. 4, therefore, the die length is determined, in the direction of the tie bar axis, as the sum of the lengths of the main molds MVD and FXD. This die length is inherent in the combination of main molds MVD and FXD. That is, there necessarily exists a length inherent in another pair of main molds which differs in length from one pair of main molds. Accordingly, the mold closing position can not be set to less than the die length inherent in the each of the main molds.
In a conventional type of die casting machine, a toggle mechanism and a link housing (not shown) are mostly employed. A conventional type of die casting machine can also employ an arrangement of a ram cylinder to clamp molds and a template to fasten the cylinder. In these types of die casting machines, the dimension of a base BS, i.e., the length of the mold clamping apparatus, can become relatively large in the opening and closing directions of the molds. Also, because it is necessary to extend the tie bar to a location of the link housing or the template, there arises a problem that the tie bar must be elongated and thickened.
Further, in medium or large size die casting machines, the die length of the molds can be large and the weight can range between a few tons to more than ten tons. More specifically, bending moment always acts downward on the moving die plate MVPL which moves on a guide due to forming a cantilever that could cause the moving die plate MVPL to turn over or tilt.